Final answer:
The arrangement of electron groups around the central carbon atom in CO2 is linear, with two electron groups that are bonding pairs arranged 180 degrees apart according to VSEPR theory.
Step-by-step explanation:
The phrase that best describes the arrangement of electron groups around the central carbon atom in CO2 is linear. According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the carbon atom in CO2 forms two double bonds, and each double bond is considered a single electron group. These two electron groups are arranged 180° apart to minimize repulsions, resulting in a linear geometry. This is designated as AX2, where 'A' represents the central atom, 'X' represents the surrounding atoms, and the '2' indicates the number of bonding pairs. Since there are no lone pairs on the central carbon atom, only bonding pairs (BP) are considered, and the lone pairs on the oxygen atoms do not influence the molecular geometry of CO2.
It is important to note that the presence of lone pairs on the central atom would lead to a different molecular geometry. For instance, if the central atom had three electron groups with no lone pairs, the molecule would adopt a trigonal planar shape with 120° angles. Conversely, four electron groups about the central atom would result in a tetrahedral geometry with approximate bond angles of 109.5°, as seen in molecules like methane (CH4).